我正在使用 Realm 来为 Android 项目保留对象。 问题是我有许多类和内部字段作为类和它们的列表的组合。 有点像
class A extends RealmObject{
@PrimaryKey long id;
B b;
}
class B extends RealmObject{
@PrimaryKey long id;
RealmList<C> cList;
}
class C extends RealmObject{
@PrimaryKey long id;
Date date;
String value;
//other fields....
}
问题是我想更新C的一些字段或者在B的RealmList中插入新的C。为了保持关系,我应该按什么顺序这样做?谁能举个真实的例子?此外,Realm 不支持 ID 的自动递增,目前我在启动时将它们设置为 currentTimeInMillis。有更好的替代方案吗?
最佳答案
让你的模型类成为
class A extends RealmObject{
@PrimaryKey
private long id;
private B b;
public A(){
//required empty constructor
}
public A(long id){
this.id = id;
}
public B getB(){
return b;
}
public void setB(B b){
this.b = b;
}
}
class B extends RealmObject{
@PrimaryKey
private long id;
private RealmList<C> cList = new RealmList<>();
public B(){
//required empty constructor
}
public B(long id){
this.id = id;
}
public RealmList<C> getCList(){
return cList;
}
public void setCList(RealmList<C> cList){
this.cList = cList;
}
}
class C extends RealmObject{
@PrimaryKey
private long id;
private Date date;
private String value;
//other fields....
public C(){
//required empty constructor
}
public C(long id){
this.id = id;
}
}
示例 - 1:创建新对象并根据层次分配它
Realm realm = Realm.getDefaultInstance();
realm.beginTransaction();
C c = new C(id);
realm.insertOrUpdate(c);
B b = new B(id);
RealmList<C> list = b.getcList();
list.add(c);
realm.insertOrUpdate(b);
A a = new A(id);
a.setB(b);
realm.insertOrUpdate(a);
realm.commitTransaction();
示例 - 2:更新数据库中的现有条目
C c = realm.where(C.class).equalTo("id", id).findFirst();
realm.beginTransaction();
c.setValue("New Value"); //setter method for value
c.insertOrUpdate();
//while updating the existing entry in the database, you need not worry about the hierarchy, Realm will maintain the same hierarchy for updates
//If you want to copy the existing entry from one object to another, you can use combination of method-1 and method-2
realm.commitTransaction();
关于android - 插入或更新的 Realm 顺序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41953956/